Alternating-current motor.



W. C. KORTHALS-ALTES ALTERNATING CURRENT MOTOR. APPLICATION mm APR. 11. ms.

1,21 9,952. Patented Mar. 20, 1917.

lnvervtior WI llem C. Kortfhalg -AH3 v His Aftornsy UNITEDLSTATES PATENT OFFICE.

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Patented Mar. 20, 1917.

Application filed April 1. 1916. Serial 10. 90,400.

vented certain new and useful Improve ments in 'Alternating-Current Motors, of which the following is a speoification.

My invention relates to alternating 'current commutator motors, and particularly to polyphase alternating current commutator motors of the brush shifting type, and has for its object to provide an improved polyphase alternating current commutator m0 tor of the brush shifting type having compound excitation,

The, particular object of my present invention is to provide a polyphase alternating current commutator motor adapted to normally operate with series characteristics but at the same time provided with means for giving the motor a relatively low no-load or light-load speed. It sometimes is necessary in certain classes of equipments, such.-

for example as printing-press machines. calendars, and the like, to operate the apparatus at a relatively low speed under rela- "tively light or varying load conditions.

Take, for example, the case of a printing press where a very low speed is necessary for feeding in the paper or for adjusting the rolls. Heretofore, high speed printing press equipments have often been provided with two motors, one of which is employed for the normal high speed operation of the apparatus, while the other, a relatively low speed motor, is employed for feeding the paper, etc. In equipments of this character the apparatus is operated at a very low speed while the paper 'is being fed in and is then run at as high a speed as practicable. Whenever the paper breaks, as frequently I occurs in practice, the high speed operation must cease, and the paper-must again be fed in with the apparatus running'at a very low speed. In two-motor equipments a clutch is provided for at will connectlng the low speed motor to the apparatus, but at the same time the high speed motor must be.

electrically disconnected from thesource of electric energy supply, or mechanically disconnected from the printing press appara'- tus. fThis necessitates a very complicated control equipment besides an expensive initial-outfit. In accordance with my present invention a single polyphase alternatin current commutator motor 'may be emp oyed for. satisfactorily running a printing press at the low speed for f g in the paper, etc, and for running'the printing press at its high normal operating speed. s

The low speed required in rinting press equipments, and thelike, mig t be obtained by a series motor, if it were not for the fact that such equipments, as a general rule, have very high static friction requiring high torque for starting with a decreasing torque v as the apparatus speeds up. A series motor would give the. uired high torque for starting, but as the oad or required torque decreased the speed -would. increase, and thus, due to therelatively li ht load after the apparatus has been sta a series mo- ;tor would speed upra idly, thereby endangering the operators w o are manually feeding the paper through the rolls. The improved motor of my present invention is in "effect a series motor having a definite vlimited low no-load or light-load speed, so that the .rmtorcan be operated under the conditions specifically mentioned hereinbefore source-of alternating currentenergy 6- by means of a suitable switch 7. The motor diagrammatically represented in the drawing is. a three-phase motor, and the stator winding 5 is wound like the primary winding of ordinary threephase induction motor. In the accompanying drawing the phases of the stator winding are represented as star-connected, .the circle 8 representin T the neutral, point of the winding, but it wi be obvious to those skilled in theart that the stator winding may be either star or delta connected;

The rotoror armature windin of the motor is a commutated winding similar to the armature winding of an ordinary direct current motor. This rotor winding and its coiiperating commutator are diagrammatically represented in the drawing by, the circle 9. A set'of stationary brushes 11, 12, and 13, and a set of movable brushes 14, 15 and 16 bear on the commutator of the rotor winding. The three brushes in each set have a polyphase arrangement, that is to say, the three brushes of each set are positioned on the commutator 120 electrical degrees apart. The movable brushes 14, 15 and 16 are preferably carried by a single brush-holder yoke 17, which may be manually movedby'a handle 18 for shifting the brushes 14, 15 and 16 with respect to the brushes 11, 12 and 13, respectively.

The stationary and movable commutator brushes are connected in pairsto the terminals of the secondary. winding 21 of a series transformer whose primary winding 20 is connected in series with the stator winding 5. Thus, one phase of the secondary winding of the series transformer is connected between brushes 11 and 14, the second phase is connected between brushes: 12 and 15, while the third phase is connected between brushes 13and 16. Movement of the brush yoke 17 thus varies the amounts of the armature winding across which the phases of the secondary winding of the series transformer are connected, and thus varies the degree of series excitation of the motor.

A polyphase autotransformer 22 is connected across the main polyphase conductors connecting the motor to the source 6. The

autotransformer 22 is thus in efiect a shunt transformed and its windings are star-coning 9 which produces a shunt excitation of The speed of the'motor' will depend on the.

transformation ratio of the 'autotransformer 22. By shifting the brushes 14, 15 and 16 away from coincidence with brushes 11, 12 and 13, respectively, a current der1ved from the series transformer 2021 by producing a series excitation.' The torque of the motor w ll now have both shunt and serles characteristics, or inother words,the

motor will operate with componnd char-" acteristics, Under such conditions it will be lmposslble for the motor to run faster than the shunt speed, since the shunt conwindin nection will cause the motor to operate as a generator and so prevent the speed of the motor rising. The shunt connection can hence be used for dynamic braking, since the shunt excitation will produce a shunt generator action in the machine if the speed rises slightly above the normal shunt speed. lit will also be evident that the shunt excitation which the motor receives from the autotransformer .22 operates to limit the noload speed of the motor. It will be obvious that the autotransformer 22 may be an ordinary transformer with independent pri-v mary and secondary windings and in either case may be star or delta connected, and further that the series transformer 20-21 may, if desired, be an autotransformer and may also be star or delta connected.

As hereinbeforc suggested the improved motor of my present invention is particularly adapted for use in equipments operating normally at relatively high speed, but in which a relatively low no-load or lightload speed is frequently required. When applied to such equipments the switch 26 will be closed when the relatively low speed is desired, as, for example, when feeding in paper in a printing-press machine. Upon the com letion of the operation requiring the relatively low speed, the switch 26 may be opened and the motor will then operate with series characteristics. Speed variations can be obtained by shifting the movable brushes 14, 15' and 16, and 1n practice these brushes will be shifted to obtain the desired speed'of operation. It will of course be understood that any suitable control apparatus may be provided in combination with my improved motor to facilitate the ordinary electrical changes in the motor plonnlections for the particular equipment in What I claim as. new and desire to secure by Letters Patent of the United States, is

1. A polypha se alternating current commutator motor having a polyphase stator winding and a commutated rotor winding, a polyphase arrangement of movable brushes and a polyphase arrangement of stationary brushes bearing on the commutator of said rotor winding, a polyphase series transformer included in the circuit of said stator winding, said movable and stationary brushes being connected to said series transformer so that varying degrees of series excitation can be produced in said rotor windp ing by movement of said movable brushes, Wlll flow through the rotor winding, thereto be connected to certain of said brushes.

2. A polyphase alternating current commutator motor having a polyphase stator and a 'commutated rotor winding, a polyp ase arrangement of movable brushes and a polyphase arrangement of stationary brushes bearing on the commutator of said rotor winding, a polyphase series transformer having its primary circuit included in the circuit of said stator winding and its secondary. circuit connected between said stationary brushes and said movable brushes so that varying degrees of series excitation can be produced in said rotor winding by moving said movable brushes, and a polyphase shunt transformer having its primary circuit connected in shunt relation to said stator winding and its secondary circuit connected to said stationary brushes.

3. A polyphase alternating current commutator motor having a polyphase field winding and a commutated armature winding, a polyphase arrangement of movable brushes and a polyphase arrangement of sta-' tionary brushes bearing onthe commutator of said armature winding, a polyphase series transformer connected between said stationarybrushes and said movable brushes so that varying degrees of series excitation can be produced in the armature winding by moving said movable brushes, and a polyphase shunt transformer adapted to be connected to certain of said brushes.

In witness whereof, I have hereunto set my hand.

WILLEM c. KORTHALS-ALTES. 

